The major goal of the application is to understand how HIV-1 antigens are presented to the humoral immune system in vitro, and thereby to devise methods to better present these antigens in the context of a HIV-1 vaccine. An important observation is that the anti-env response persists during the course of HIV-1 infection, even when anti-gag responses are lost. The applicants hypothesize that the anti-gag response decays due to the loss of specific T-cell help. A corollary is that anti-env antibodies can be generated relatively independently of classical T-cell help and are retained during disease progression. However, these natural antigen presentation pathways for gpl20 and gp4l are completely unknown. The applicants plan to explore the role of dendritic cells in the presentation of env antigens to B-cells, and thence in the production of neutralizing antibodies. The neutralizing antibody response to HIV-1 is important, yet how such antibodies are elicited in vivo is poorly understood. It is known that the anti-gpl20 response is retained when the anti-gag response is lost, but it is not known why. Nor is it known how antibodies to gpl20 are generated. These gaps in our knowledge have implications not only for understanding HIV-1 pathogenesis, but also for the rational development of vaccines based wholly or in part on neutralizing antibodies. The specific aim is to explore how anti-env responses are generated in culture, in particular, to define the antigen-presenting cell and T-helper cell requirements. The role of the dendritic cell in the B-cell response will be a major emphasis. The development of both anti-env binding and virus-neutralizing antibody responses will also be monitored.